Buildings in Teplice have quite a variety of architectural styles to offer. You can see remains of the Romanesque church in the garden of the castle, the town hall and parts of the castle and the neighbouring churches provide some Gothic relicts, there is a few Renaissance and Baroque as well.
Most parts of the town, however, are excellent examples for ensembles of Empire style, classicistic architecture, and also examples of the Neo-styles of the 19th century are well preserved. Some of my favourites are the Art Nouveau townhouses.
Getting in and out of Teplice you'll also notice (and also from viewpoints in the centre) the large and ugly apartment blocks in the suburbs, erected in the communist era. Don't let these spoil your visit.
Watch out that you do not miss the oldest part of Teplice! If you arrive by train or bus you have to cross the centre of the town (with town hall and market square) to get to Zamecke namesti/castle square.
This square is really beautiful. The castle at the southern side, two churches at the eastern, old townhouses at the northern side and finally the wonderful hotel Prince de Ligne at the western side. The landmark, however, is the Baroque St. Trinity column in the centre. An ensemble, grown over centuries and very picturesque.
Favorite thing: Teplice is a town with some absolutely beautiful gardens. While the gardens in the spa area, which stretches from Beethoven spa centre to Neubad/Nove lazne, are designed and please the visitor's eyes with blooming flowers, statues, fountains etc. there are also large gardens in "English" style - in the back of the castle and on top of Letna hill as well as Janackovy sady on the hill above Kamenny lazne.